Cell Wall of Acid Fast Bacteria @ Contains an inner peptidoglycan layer and an outer membrane layer....

Cell Wall of Acid Fast Bacteria

@Contains an inner peptidoglycan layer and an

outer membrane layer .

@ The inner peptidoglycan layer is joined to the cell membrane by the Phosphatidyinositol mannosides (PIM) chain

@Also the inner peptidoglycan layer is joined

to an arabinogalactan layer (arabinose and

galactose) by a lipoarabinomannan chain .

@The arabinogalactan layer is attached directly to the mycolic acids layer .

@The mycolic acids layer is followed by a layer of acyl lipids.

@Porins are found to transport the hydrophilic

molecules through the outer membrane layer .

@Proteins are located on the surface of cell

@Mycolic acids are esterified to form polysaccharides (wax D) and glycolipids.

@Lipids are responsible for: * Acid fast staining

* Stickiness of mycobacteria

Bacterial L-Forms

@Loss of cell wall because murein for wall

synthesis is absent

@Spheroplasts: gram negative L-forms

@Protoplasts: gram positive L-forms

@Origin : * Spontaneous (Streptobacillus,

Bacteroides) *Presence of penicillin or lysozyme * Destruction of wall by complement

* Absence of nutrient for wall synthesis

@No pathological or clinical significance.

Bacterial Cell MembraneStructure:

@ Composed of 3 layers:

@ 2 phospholipids layers with phosphate heads and lipid tails.

@ They are hydrophilic at their phosphate heads and hydrophobic at their lipid tails.

@ The hydrophobic lipid tails point inwards and the hydrophilic phosphate heads point outwards. @ Glycoproteins point outwards & attached to carbohydrate chain

@ Integral proteins help to anchor the cytoskeleton in place.

@ Transmembrane proteins have enzymatic activity & catalyze chemical reactions

@ The third layer is the hydrophobic region.

@ It contains proteins (70%) and lipids (30%)

@ ٍCM: semipermeable to nutrients, water, salts

@ Folded towards cytoplasm to form mesosome

Functions of Cell Membrane

@ Forms an osmotic barrier between cytoplasm and environment

@ Transport of: # Respiratory electrons # Nutrients inside cell.

# Waste product outside cell

@ Synthesis and transfer of peptidoglycan, teichoic acids, & other contents of cell wall

@ Secretion of extracellular enzymes and toxins

@ Segregation of chromosomal and plasmid DNA

into daughter cells.

Mesosomes

@ Mainly invaginations of cell membrane@ Functions include: # Involved in nuclear division # Provide respiratory enzymes # Excretion of material outside the cell # Involved in cell wall synthesis # Involved in cell wall division

@ Convoluted & formed of lamellae or vesicles.

@ Developed in mycobacteria, E. coli, Bacillus

@ May join cell wall or nuclear body

Cytoplasm

@ Contains: water, ions, metabolites, proteins, nucleic acids, storage granules, ribosomes.

@ Ribosomes actively translating messenger RNA into proteins.

@ Storage granules serve as reserves of energy

and nutrients.

@ Metachromatic (volutin) granules are reserves

of high energy phosphates in corynebacteria.

@ Contains the bacterial chromosome as a single circular molecule.

Bacterial Nucleoid

@Bacterial chromosomal DNA is not enclosed

by an envelope

@The chromosomal DNA molecule is 1.6 mm in

a form of coil .

@ Plasmid is a separate DNA molecule that can replicate independently

@ Plasmids are double-stranded and circular. Their number can range from 1 to thousands.

@ Plasmids can integrate and replicate with bacterial cells.

Endospores

@ Induced by: Changes of pH, temp., oxygen tension, nutrients, waste products, moisture, minerals (Ca++, Mn, K).

@ Differences from vegetative cells: # More resistant to heat, disinfectants, dryness, starvation # Low water content (5 - 20%) # Thick, impermeable coat # Low metabolic activity # Contain Ca++ and dipicolinic acid

Endospore Structure

@Endospores form within a vegetative bacterial cell

@Exosporium: a thin delicate covering

@ Spore coat: thick layer of protein & keratin

@ Cortex: made of peptidoglycan

@ Core wall

@ Core: contains ribosomes and nucleoid

Cycle of spore formation and germination:

@ Bacterium makes a copy of its chromosome DNA & the bacterial cell membrane begins invaginating inward until there’s a little daughter cell within the mother cell.

@ Next, membrane of mother cell surrounds the daughter cell. Then two membrane layers will surround the daughter cell.

@ Then a thick peptidoglycan wall forms and a tough outer protein coat forms around all daughter cell, which is now spore.